Focus of high-power microwaves with positive and negative zone plate to increase the receiving power in axial virtual cathode oscillator

We investigated an axial vircator, constructed in a pulsed power generator, called Chundoong, and simulated by a three-dimensional particle-in-cell simulation code, MAGIC. We attempted to increase the receiving power of generated microwaves by directing them at a desired focal point. To do so, a positive and negative zone plates (ZPs) are constructed at main frequency 3.5 GHz, and its focal length is 18.8 cm. The power generated from the virtual cathode is 0.72 GW, from which 24.6 kW is received by receiving antenna without a ZP. The receiving power increased significantly to 45.4 kW (92.6%) and 47.5 kW (84.5%) with positive and negative ZPs, respectively. In addition, both positive and negative ZPs have similar focusing properties for the generated microwaves. The ZP contributes significantly to increasing the receiving power. These findings might be useful for real applications to increase the receiving power at a desired focal point.